Stair tread minimum thickness

[David Helm]

The change to 73/4 max riser height just took place this past year. Most communities now use IRC which put this change into effect.

[Don Alexander]

if you have the space try to keep your risers to no more than 7" when you get taller than that it quickly gets to be an uncomfortable step especially for women and children (shorter men as well)

as for dimension of the stock involved , a good rule of thumb for stairs is that if it has enough flex in it to feel it you need more wood , either that 3rd stringer (usually the most effective method) or bigger dimensions on the 2 stringers and treads .

stairs are not the place to get cheap on the amount of material used particularly not if you do not want to constantly wonder if they are going to hold the load

IMHO you will never be sorry if you "overbuild" a bit on stairs

[Jeff Gunter]

As others have said, check with your building inspector. The IRC 2006 Visual Guide lays out the min/max radii for the round overs.
My gut reaction is to add a third stringer as others have suggested. You could probably work out the L/360 for red oak on a 36" span to know what thickness you need ... of you can probably add another stringer in the same amount of time unless you have the right docs handy.
I put in 7/8" q.s. r.o. treads on a 42" wide stair case with 3 stringers and have had no problem. I cut a rabbet on the bottom edge of the risers and fastened (glued and screwed) each riser to the tread below making an ell shape. No squeaks, no creaks, feels solid. In my area the building inspector uses the visual guide for reference.

[Sean Rainaldi]

Thanks all,

David or anyone, from my dimensions, it looks like I will have to go with 12 risers, 7.84" in height and I think a 9" tread which is what we have now - 9" plus an extra inch for the overhang makes it a 10 inch tread but 9 actual.

I have a total rise of 94 1/8" this would make a total run of 99". This is the stairway into our basement.

If I go with an extra riser that would make 7 1/4" risers and I don't think my gal would like that she is more used to our current 7 3/4 inch riser height, she has arthritis in the knees and I don't want to change too much since she is used to it - afraid she might lose her balance or trip.

I'm going to use 2 x 12 stringers - my calculations tell me I would have a stringer length of 11.36"' with a stair angle of about 43.5 degrees - can anyone confirm my stringer length - angle?

Think the inspector would get picky about an extra .09" riser height?
.

[bill mullin]

If you have the room, I would consider making the treads longer, and adding another riser/tread. The stair would be less steep and easier to walk for your lady.
I find anything between 7 1/4 and 7 3/4 comfortable to walk. Less than 7 feels like taking baby steps, and 8 is easy to trip over, IMO.

[scott vroom]

Sean, a simple call to your local city or county building department will get you your answer. Lots of good inputs on this thread, but your question is code related and only your local jurisdiction can provide an accurate answer.

[Sean Rainaldi]

Thanks Bill,

Unfortunately I don't have the room because as it is already, I will have to cut out and box in one of the floor joists to get my 80 inch minimum headroom at the bottom of the stairs and in doing so lose part of our cold air return - I have three joist cavaties panned as cold air return cavaties and we will be losing one of those three with this stair modification as it is, and I will have to move that to the end of the basement.

The stair case originally went half way down into the basement, had a landing mid way, and did a 180 for other treads. The problem is our room is only 14 feet wide and the stairwell took a big bite out of the floor plan - the first thing you see when walking in from the front door is a huge stair well and this gives us only about 40 inches from front door to the stair well.

So we decided to have the stairs go straight down into the basement to open up the main floor.

These are small homes, only about 1700 square feet built over 50 years ago. So If I add more risers and or increase tread length, we will lose a second cold air return cavity - our cold air return is directly over head at the bottom of the stairs.coming down the stairs. So the most room I can afford is to cut into the first joist of the existing cold air return cavities and move that cavity to the other end of the room and box in that one joist, and that only allows for 12 risers, 11 treads at 9” deep treads, and in doing that I get my minimum 80 inch headroom at the bottom of the stairs.

As it is now, the number of risers and treads and dimensions of such is about the same as the original stair case, the only difference is that it will go straight down into the basement and the stairwell will be about 16 inches longer and half the width.

[Steve Schoene]

If you go to your local lumber yard you will find stair treads stocked as a commodity. That's a good deal since they already have the proper bullnose and are generally clear material. The ones I've seen are typically 1" (nominally 5/4). Better, and likely less expensive, to add a middle stringer than to worry over the thickness of the tread.

Rise height of 7 !/4" generally makes for a very comfortable stair, if you have the length for the additional run--but stairs to basements often don't have the room.

[Tom Grant]

When I "moved" the stairs in our house, I used 1.75 x 10" LVL for my three stringers. This is a great use of LVL - Flat, straight and stable. I ended up with a 7 1/8" rise (x15). We still have the "temporary" 1 inch pre-made LVL treads I put on. One of these days I'll replace them with some real wood.

[Sean Rainaldi]

Thanks Steve I'll check it out, I think I will use 3/4 inch baltic under 3/4 inch oak tongue and groove flooring though for the sole reason I have lots of it around here and want to save some $. I checked out Lumber Liquidators they wanted 20 bucks a tread for 36 x 10 white oak.

I think these will be my last questions in this thread, I am getting ready to build, these are mainly construction related:

1.) For the stringers, what would be the best way to attach the thrust block or kick plate 2 x 4 to the concrete floor? (when I say thrust block I mean the piece that attaches to the floor and which the notch in the stringer rests upon). I was thinking of using Strong Tie fasteners – would that be sufficient? Or should I use one of those .22 nail guns and shoot nails into the board / cement? Or is there a better, more secure method?

2.) Secondly we have the 2x8 joists and I am building the stairs out of 2x12 stringers. Having not cut the stringers yet, I am assuming that when I butt up the stringer to the joists to attach that there will be a protrusion of the underside of the stringer below the joist and I read that this is a no no. Does this matter? If so, what is the best way to attach a 2 x 12 stringer to a 2 x 8 floor joist? I am assuming I will have to attach some kind of a header to the joist so the stringer top end can span the entire header width – is this the right way to do it? Would ¾ inch plywood be good or is there another way I should do it? This was not an issue for the old stairs because the old stringers were of 2 x 10 material.

3.) Do I need any studs between floor and stringers to support the stringers mid way through their span?

4.) Am I forgetting anything else in the construction – any other advice or ideas?

Thanks for all your input folks!

[David Helm]

If your concrete floor is old it may be too hard for the .22 powered nails. A better way is to either drill 1/4 inch holes and use split pins or to use expansion bolts. Both methods would be more secure than gun driven nails. It is never a bad idea to put midspan support on stair stringers. I have always done this when the vertical increase is 8 feet. Just makes for sturdier stairs.

[Sean Rainaldi]

Thanks David,

Actually I need to make a correction in 1 above I meant Tapcon cement anchors for the thrust block, not strong tie. I have some tapcom 3/16" concrete anchors and their drill bit. Think this would be OK?

And for 2 the home depot guy suggested using the Simpson strong tie joist hangars for the stringers, the LSU28 for 8 inch joists - these hangars are adjustable for any slope up to 45 degrees. What do you think?

[David Thompson 27577]

For 36" wide treads, use three stringers.

And since you'll be using three stringers, tread thickness might be less of an issue. FWIW, traditional stair treads (pine or hardwood) are made from 5/4 stock (finished thickness 1").

Be careful when laying out the cuts for the stingers -- a common mistake is to forget the difference that the tread thickness makes for the bottom and top steps.

[David Helm]

The joist hanger is probably OK. The main thing that keeps the stairs in place is the thrust plate at the bottom. Not to say that there shouldn't be positive attachment at the top. Better to go strong than not.

[Henry Ambrose]

Assuming you don't need a flat floor access to the under stair area, tie the mid-point stud supports to the floor end of the stringers. Screw those plates down to the floor with tapcons. Your 3/16 will be fine and you will have loads of holding power with lots of tapcons in shear. Screw the stringer ends and support studs to the plates. Do all three stringers this way. Your stairs won't move.

I'll also add that unless you are altering the configuration or footprint of the stairs you may not need a permit or inspection. Local rules may say otherwise.

If you are altering the configuration there is an Excel spread sheet on the web that allows you to specify all the stair parts and calculates the rise and run and generates a cutting plan.

"Stair Stringer Design Calculator Spreadsheet"

Here it is: http://www.shalla.net/